JPH0663108B2 - Manufacturing method of magnesium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing magnesium by electrolyzing magnesium chloride to produce magnesium, particularly the production of magnesium chloride to be supplied to an electrolytic cell and the electrolysis of magnesium to produce magnesium. The present invention relates to a highly efficient method for producing magnesium, which is combined with a process for producing magnesium.

(Prior art) Magnesium is the lightest metal material among practical metals, and its use is as an inoculant for the production of alloys with aluminum, for the production of ductile cast iron, as a reducing agent for the production of titanium from titanium tetrachloride, etc. The number is increasing.

Currently, 90% or more of magnesium is produced by an electrolytic method in which magnesium chloride is electrolyzed, and the rest is a reduction method using silicon.

Conventionally, the following methods 1) to 4) have been adopted as a method for producing magnesium chloride to be subjected to magnesium electrolysis.

1) Add ammonium chloride to hydrous magnesium chloride,
Method of heating dehydration 2) Method of heating dehydration of carnallite (MgCl ₂ · KCl 6H ₂ O) 3) Dissolving water-containing magnesium chloride (MgCl ₂ · nH ₂ O) by adding hydrochloric acid to obtain n = 1.25 to 2 Method of evaporating and concentrating until it becomes dehydrated, and electrolyzing it as it is (Dow method) 4) Mixing magnesia (MgO) and carbon material such as pitch to make briquettes, chlorinating magnesia with chlorine, and dehydrating Method for Obtaining Magnesium Chloride (Problem to be Solved by the Invention) However, the methods 1) and 4) have complicated manufacturing steps and low productivity, and the method 2) requires a large amount of energy for heating dehydration. Carnalite (MgCl ₂ ·
There was a problem that KCl generated by the decomposition of (KCl ・ 6H ₂ O) was deposited in the electrolytic cell and needs to be removed regularly, and that the deposit could only be used as fertilizer. . In addition, the Dow method of 3) above involves the decomposition of the water contained during electrolysis, which causes the graphite anode to be heavily consumed and requires a special electrolytic cell, and the chlorine concentration in the produced gas is low. There was a problem that it was difficult to reuse.

Further, in any of the above-mentioned conventional methods, since magnesium chloride having a very high hygroscopicity is taken out as a solid and handled, magnesium chloride absorbs moisture in the atmosphere, and this moisture is simultaneously generated during magnesium chloride electrolysis. It is electrolyzed and part of the electrolysis current is consumed. Further, the oxygen generated by the electrolysis of water reacts with magnesium deposited on the cathode to become MgO, which is deposited on the bottom of the electrolytic cell and solidified to generate sludge. Therefore, it is necessary to take thorough technical measures in handling the supply of magnesium chloride to the electrolytic cell.

It is an object of the present invention to produce magnesium chloride without the above-mentioned problems in the prior art and to provide a method for producing magnesium using the magnesium chloride.

(Means for Solving the Problems) The gist of the present invention is to extract an electrolytic bath salt having a reduced concentration of magnesium chloride from an electrolytic bath for electrolyzing magnesium chloride to produce magnesium, and to form a solid powder in the electrolytic bath salt. Magnesium oxide or / and magnesium carbonate of is suspended, and a gas containing chlorine is passed through this suspension to react magnesium oxide or / and magnesium carbonate with chlorine to produce magnesium chloride. The method for producing magnesium is characterized in that the elevated electrolytic bath salt is returned to the electrolytic cell for electrolysis.

The extracted electrolytic bath salt contains solid powdery magnesium oxide,
Suspending one or two of magnesium carbonate. These may be added to the bath in the form of MgO, MgCO ₃ , but MgO, MgCO ₃
An ore such as magnesite containing CO ₃ or a primary product such as heavy burned magnesia or light burned magnesia may be added.

When MgCO ₃ is added to the bath, it decomposes by the reaction MgCO ₃ → MgO + CO ₂ (1) to produce MgO in the bath, which is converted to MgCl ₂ by the equation (2) described later. As the magnesium oxide, those having a relatively high MgO purity, such as magnesia obtained by burning magnesite (magnesium carbonate) or magnesium hydroxide, are suitable for use.

Gases containing chlorine include chlorine gas (Cl ₂ ), mixed gas of chlorine and carbon monoxide (CO), phosgene (COCl ₂ ).
Etc., or a gas in which a carbon-containing substance is mixed with these gases. As the carbon-containing substance, coke powder,
Besides methane (CH _4), ethane and petroleum pitch (C
A gas such as ₂ H ₆ ) can also be used. When the carbon-containing substance is a solid powder such as coke powder, good results can be obtained even if these substances are directly added and suspended in the molten salt.

(Operation) First, the production of magnesium chloride, which is the first step of the method of the present invention, will be described.

In this step, the fact that magnesium oxide reacts with chlorine and changes to magnesium chloride based on the reaction formula MgO + Cl ₂ → MgCl ₂ + 1 / 2O ₂ (2) below (2) is used.

When a mixed gas of chlorine and carbon monoxide is used, magnesium chloride is produced by the following reaction formula (3) MgO + Cl ₂ + CO → MgCl ₂ + CO ₂ (3). When the carbon-containing substance is added to the gas to be fed, the molten salt, or both, for example, the reaction formulas of (4) and (5) below are MgO + Cl ₂ + 1 / 2C → MgCl ₂ + 1 / 2CO ₂ (4) 4MgO + 4Cl ₂ + CH ₄ → 4MgCl ₂ + CO ₂ + 2H ₂ O (5) produces magnesium chloride.

The reaction between magnesium oxide and chlorine in the presence of a carbon-containing substance is an exothermic reaction. Therefore, the carbon-containing substance has the effect of increasing the temperature of the electrolytic bath salt and promoting the reaction.

Next, the step of obtaining magnesium from magnesium chloride will be described.

The accompanying drawings are schematic cross-sectional views showing an example of an apparatus for carrying out the method for producing magnesium according to the present invention. This apparatus comprises a chlorination furnace 1 and a magnesium chloride electrolytic cell 10 for electrolyzing magnesium chloride to produce magnesium, and a conduit 20 for introducing the magnesium chloride produced in the chlorination furnace 1 into the electrolytic cell 10.
And a conduit 9 for supplying molten salt in the electrolytic cell 10, that is, electrolytic bath salt 11 to the chlorination furnace 1, and chlorine gas 16 generated in the electrolytic cell 10.
Is connected to the gas inlet 8 of the chlorination furnace 1.

The chlorination furnace 1 and its upper lid 2 are made of refractory material, and a raw material charging port 4 for charging a raw material magnesium oxide (hereinafter, referred to as using magnesium oxide) to the upper part of the furnace wall of the chlorination furnace 1. However, the bottom of the chlorination furnace 1 is provided with a gas inlet 8 for feeding a chlorine-containing gas. The upper lid 2 is provided with a gas discharge port 3 for discharging the gas after the chlorine-containing gas fed from the gas feed port 8 reacts with magnesium oxide.

An anode 13 and a cathode 12 are attached to the magnesium chloride electrolytic cell 10, and a partition wall 14 is provided between the anode 13 and the cathode 12 to divide the upper part of the electrolytic cell 10 into an anode side and a cathode side.

In order to produce magnesium with the apparatus configured as described above, first, the chlorination furnace 1 is provided with a magnesium chloride electrolytic cell.
An electrolytic bath salt 11 is supplied from 10 via a conduit 9. This is bath salt 5. Next, the raw material magnesium oxide is put into the chlorination furnace 1 through the raw material charging port 4, and suspended in the bath salt 5 by a method such as mechanical stirring or gas bubbling. Then, a chlorine-containing gas is fed through the gas inlet 8 to raise the bath salt 5 as bubbles 6 and react with the suspended magnesium oxide 7. Since the chlorine-containing gas is more reactive when it becomes the finest bubbles 6, it is better to attach a porous plate or a small-hole nozzle to the gas inlet 8.

In this way, magnesium oxide 7 and chlorine react in the suspension bath salt 5 as shown in the above formula (2) to produce magnesium chloride, which is dissolved in the bath salt 5 to increase the concentration of magnesium chloride. In this case, a carbon-containing substance (calcine coke, etc.) may be added simultaneously to the gas or / and the bath salt to be sent, or the gas to be sent may be a mixed gas of chlorine and carbon monoxide. . The reacted gas is discharged from the gas discharge port 3, but if there is unreacted chlorine, it may be recovered.

Next, the bath salt 5 having an increased magnesium chloride concentration is returned to the electrolytic cell 10 via the conduit 20. The bath salt 5 or electrolytic bath salt 11 returned to the electrolytic cell 10 undergoes electrolysis to produce carbon 16 at the anode 13 and magnesium 15 at the cathode 12. In this way, magnesium can be produced. Further, the generated chlorine 16 is passed through a conduit 18 to be pressurized by a compressor 17 and is passed through a conduit 19 and a gas inlet 8 to the chlorination furnace 1
It can be sent to and reused.

The electrolytic bath salt 11 whose electrolysis has reduced the concentration of magnesium chloride is transferred again to the chlorination furnace 1 via the conduit 9, and magnesium oxide is added to carry out carbonization again. By repeating the above operation, production of magnesium chloride and electrolysis can be continuously performed.

When chlorinating magnesium oxide by the above-mentioned method of the present invention, the reaction rate starts to decrease when the concentration of magnesium oxide in the bath salt 5 becomes 5% or less, and the reaction rate decreases as the concentration decreases. Especially when it is less than 1%, it drops sharply. Therefore, while measuring the unreacted chlorine concentration, the reaction is stopped immediately before the chlorine reaction rate sharply deteriorates, that is, before the magnesium oxide concentration becomes 1% or less, and the unreacted magnesium oxide is allowed to reach the bottom of the furnace 1 by spontaneous precipitation. It is sufficient that the chlorination furnace 1 is allowed to deposit and only the supernatant liquid is taken out from the chlorination furnace 1 as electrolytic bath salt.

When chlorinating magnesium oxide, the higher the concentration of magnesium chloride, the slower the reaction rate becomes. Especially, when magnesium chloride exceeds 70%, the tendency becomes remarkable, so the concentration of magnesium chloride in bath salt 5 is required. It should be avoided to raise it more than the above.

In the above description, the case where magnesium oxide is used has been described, but the same applies when magnesium carbonate is used or magnesium carbonate and magnesium oxide are mixed and used. Furthermore, the same applies in principle when using an ore containing magnesium oxide or magnesium carbonate.

The magnesium produced by the method of the present invention can be used to produce titanium (Ti) by reducing titanium tetrachloride (TiCl ₄ ) according to the following formula (6).

TiCl ₄ + 2Mg → Ti + 2MgCl ₂ (6) Therefore, a facility for reducing titanium tetrachloride can be further provided in addition to the facility shown in the attached drawing to obtain high-purity magnesium chloride together with titanium by the formula (6).

Example 1 In the apparatus having the configuration shown in the attached drawing, first, a refractory chlorination furnace (inner diameter 50 cm, height 2.5 m) with a porous plate attached to the lower gas inlet was placed in an electrolyzer. Electrolytic bath salt (MgCl ₂ : 15 with reduced magnesium chloride concentration due to electrolysis)
%, NaCl: 50%, CaCl ₂ : 35%) 500 kg and kept at 800 ° C. The temperature of the electrolytic bath is usually 700 ° C. or lower, but the reaction between magnesium oxide and chlorine is preferably higher, so the temperature was raised by a heating device (not shown).

100 kg of magnesia (MgO: 90%, under 100 mesh)
Was charged, and argon gas was passed through from the bottom of the furnace to suspend magnesia in the bath salt. Then, the argon gas was replaced with chlorine gas, and the mixture was fed at a flow rate of 150 Nl / min for about 6 hours. Magnesium chloride is produced by the reaction between magnesia and chlorine,
The magnesium chloride concentration in the bath salt increased to 36.5%.

After the unreacted magnesia was separated by sedimentation, 600 kg of bath salt was returned to the electrolytic cell and subjected to electrolysis, whereupon magnesium and chlorine were produced as in the case of ordinary electrolytic bath salt.

From this electrolyzer, 400 kg of electrolytic bath salt (eg MgCl ₂ : 15%) whose magnesium chloride concentration has been reduced by electrolysis is supplied again to the above-mentioned chlorination furnace in which about 100 kg of bath salt remains,
Magnesia was added and chlorination could continue as before.

[Example 2] Under the same conditions as in Example 1, except that petroleum coke (under 200 mesh sieve) was suspended together with magnesia charged in a chlorination furnace, and chlorine gas was passed for 6 hours for chlorination. . After clarification of the bath salt, 600 kg was transferred to an electrolytic cell and subjected to electrolysis. The magnesium chloride concentration of this bath salt was 38.0%.

Electrolysis was performed using this bath salt, and magnesium and chlorine could be obtained without any trouble.

[Example 3] Under the same conditions as in Example 1, except that carbon monoxide was mixed in a chlorine gas at a ratio of 1: 1 and the mixture was fed for 6 hours. After clarifying the bath salt, 600 kg was transferred to an electrolytic cell and subjected to electrolysis. At this time, the magnesium chloride concentration was 40.0%.

The production of magnesium using this bath salt was also successful.

[Example 4] Using the apparatus used in Example 1, 100 kg of magnesium carbonate was charged into the bath salt in the chlorination furnace in place of magnesia.
The bath salt composition, temperature, and chlorine gas flow rate were the same as in Example 1. The magnesium chloride concentration of the bath salt increased to 29.5% after passing chlorine gas for about 9 hours.

Electrolysis was performed using this bath salt, and magnesium and chlorine could be obtained without any trouble.

[Example 5] The magnesium chloride electrolysis was operated by adjusting the current and time so that only the amount of magnesium chloride produced by the method of Example 1 was electrolyzed. As a result of continuous operation for about 3 months, the current efficiency was increased by about 2% compared to the conventional method of supplying magnesium chloride as a solid to the electrolytic cell, which is due to the deposition of magnesia at the bottom of the electrolytic cell. 35% sludge production
Diminished.

The increase in current efficiency and the decrease in the amount of sludge produced are due to the fact that magnesium chloride, which has a strong hygroscopic property, could be handled without taking it out of the system.

(Effects of the Invention) As described above, magnesium oxide or / and magnesium carbonate in the form of solid powder are reacted with chlorine in an electrolytic bath salt to produce magnesium chloride, and an electrolytic bath in which this magnesium chloride concentration is increased. By using the magnesium production method of the present invention in which the salt is electrolyzed to produce magnesium, chlorination and electrolysis can be repeated by circulating the electrolytic bath salt. Therefore, it is not necessary to take out magnesium chloride as a solid out of the system, the operation is simple, and the conventional problems associated with moisture absorption of solid magnesium chloride do not occur. Further, it is possible to generate a necessary amount of magnesium chloride corresponding to the amount of electrolysis, that is, the amount of magnesium produced,
Its quality is also stable.

[Brief description of drawings]

The accompanying drawings are schematic cross-sectional views showing the configuration of an example of an apparatus for carrying out the method of the present invention.

Claims (3)

[Claims] 1. An electrolytic bath salt having a reduced concentration of magnesium chloride is extracted from an electrolytic cell for producing magnesium by electrolyzing magnesium chloride, and solid powdery magnesium oxide or / and magnesium carbonate is suspended in the electrolytic bath salt. Then, a gas containing chlorine is passed through this suspension to react magnesium oxide or / and magnesium carbonate with chlorine to produce magnesium chloride, and the electrolytic bath salt having a high magnesium chloride concentration is added to the above electrolytic bath. A method for producing magnesium, characterized in that the method is carried out by returning to electrolysis. 2. The method for producing magnesium according to claim 1, wherein the gas passed through the suspension is a mixed gas of chlorine and carbon monoxide. 3. The method for producing magnesium according to claim 1, wherein the carbon-containing substance is added to the gas or / and the electrolytic bath salt which is passed through the suspension.